The same areas – linked to motivation, attention, and judgment – lit up in close friends. From the results, researchers were even able to predict which participants were friends – and their guesses were spot on.

The study raises the question: do people seek out friends who think like them? Or do friends become more alike over time? "We think both are happening," author Adam Kleinbaum told Business Insider. Having close friends with similar brain activity "may be rewarding because it reinforces one's own values, opinions, and interests".

Related: 5 unconventional films about female friendship that you might not have watched (Provided by Harper's Bazaar UK)